To meet the demand for wireless data traffic having increased since deployment of 4th generation (4G) communication systems, efforts have been made to develop an improved 5th generation (5G) or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called a ‘Beyond 4G Network’ or a ‘Post LTE System’.
The 5G communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higher data rates. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G communication systems.
In addition, in 5G communication systems, development for system network improvement is under way based on advanced small cells, cloud Radio Access Networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), reception-end interference cancellation and the like.
In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and sliding window superposition coding (SWSC) as an advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) as an advanced access technology have been developed.
The rapid development of information industry, particularly the increasing demand from the mobile Internet and the Internet of Things (IoT), brings about unprecedented challenges in the future mobile communications technology. According to the ITU-R M. [IMT.BEYOND 2020. TRAFFIC] issued by the International Telecommunication Union (ITU), it can be expected that, by 2020, mobile services traffic will grow nearly 1,000 times as compared with that in 2010 (4G era), and the number of user apparatuses connections will also be over 17 billion, and with a vast number of IoT devices gradually expand into the mobile communication network, the number of connected apparatuses will be even more astonishing. In response to this unprecedented challenge, the communications industry and academia have prepared for 2020s by launching an extensive study of the fifth generation of mobile communications technology (5G). Currently, in ITU-R M. [IMT.VISION] from ITU, the framework and overall objectives of the future 5G have been discussed, where the demands outlook, application scenarios and various important performance indexes of 5G have been described in detail. In terms of new demands in 5G, the ITU-R M. [IM FUTURE TECHNOLOGY TRENDS] from ITU provides information related to the 5G technology trends, which is intended to address prominent issues such as significant improvement on system throughput, consistency of the user experience, scalability so as to support IoT, delay, energy efficiency, cost, network flexibility, support for new services and flexible spectrum utilization, etc.
The demand of supporting massive Machine-Type Communication (mMTC) is proposed for 5G. The connection density will reach millions of connections per square kilometer, considerably higher than the link density supported by the existing standards. The existing orthogonal multiple access modes, for example, Orthogonal Frequency Division Multiple Access (OFDMA), cannot satisfy the demand of millions of connections to be achieved by mMTC in 5G. To improve the capacity of the multiple access technology, some Non-orthogonal Multiple Access (NoMA) technologies have been proposed, and discussed as the potential 5G key technologies in the 3GPP standard conferences. Among those technologies, CDMA-based access modes such as Sparse Code Multiple Access (SCMA), Pattern Defined Multiple Access (PDMA) and Multi-user Shared Access (MUSA), and interleaving-based access modes such as Interleave Division Multiple Access (IDMA) and Interleave-Grid Multiple Access (IGMA), are included. When compared with the orthogonal multiple access modes, by using non-orthogonal access resources, for example, non-orthogonal codebooks, interleaved sequences or more, those access technologies can allow more users to access on the limited time-frequency resources, so that the number of apparatuses connected in a unit area is significantly increased, and the demands of massive scenarios in 5G are satisfied.
Terminals in mMTC have special requirements on the cost and power consumption. Generally, terminals in mMTC scenarios are low in cost and require long battery life. The requirement on the UE life in mMTC scenarios was proposed by the 3GPP in [TR38.913:Study on scenarios and requirements for next generation access technologies]. The UE should last for 15 years on the premise of satisfying a certain amount of uplink and downlink data transmission, without charging. This proposes high requirements on the power consumption of mMTC terminals. Considering that the Peak-to-Average Power Ratio (PAPR) of the output signals has great influence on the power consumption of terminals, the lower the PAPR, the lower the power consumption.